Development of a many-electron mixed quantum/classical simulation algorithm and application to condensed-phase solutes' electronic structure and dynamics

Understanding how the properties of a chemical species change when it is dissolved in a liquid solvent is fundamental to chemistry. Interactions between a solute and condensed-phase environments primarily affect the valence electrons of the solute, thereby modifying its chemical properties. For example, a diatomic molecule dissolved in a liquid vibrates differently than when it is an isolated species. In some cases, the solvent dramatically alters the electronic properties of the solute giving rise to entirely new quantum states of the electrons that did not exist in the absence of the solvent. This behavior is observed for anionic solutes which, due to solvent interactions, exhibit new electronic excited states that are called Charge-Transfer-To-Solvent (CTTS) states. A detailed picture of how a solvent gives rise to these two phenomena (the modulation of a solute's vibrational properties or the introduction of new electronic states) based on first-principles physics is lacking, due in part to the computational difficulties of simulating the quantum mechanics of a liquid environment. In this Dissertation, I present the two-electron Fourier-grid (2EFG) method: a new quantum mechanical simulation method that is particularly suited to studying electronic properties of solutes in condensed-phase environments. The central idea in the method is to represent electronic wavefunctions on a six-dimensional grid. In this way, electronic interactions are treated at a high level---the method generates essentially exact wavefunctions for two-electron problems. In addition to being highly accurate, the use of a grid makes the method particularly efficient. With the 2EFG, we then explore the nature of the CTTS states of a sodium anion (sodide) in liquid tetrahydrofuran (THF). The simulations predict that the CTTS states of sodide arise due to both a favorable orientation of THF around sodide and naturally-occurring voids in THF. Many aspects of spectroscopic experiments on sodide can then be understood in light of the details of the CTTS states. We also explore the vibrational properties of diatomic sodium in liquid Ar. Even though Ar is an apolar liquid, the interaction of multiple solvent atoms produces large dipole moments on the sodium dimer. These interactions also dramatically change the dimer's bond vibration relative to the gas phase. These effects are not seen in classical simulations, highlighting the importance of many-body quantum effects in the solute-solvent interactions.